In an inkjet image forming device, when clogging of nozzles of recording heads to eject ink occurs or air bubbles come into ink before being ejected around the nozzles, the ink ejection from the nozzles is sometimes prevented, leading to poor image formation. Such an inkjet image forming device thus needs maintenance to remove clogging of the nozzles and to remove air bubbles from the ink.
As the maintenance method, a method called pressure purge is known. In the pressure purge, the ink in the nozzles is pressurized to be ejected from the nozzles at the timing other than the timing of image formation and thereby clogging of the nozzles is removed. A method called suction purge is also known for the maintenance using a suction part, which is separately provided, to suck the ink out of the nozzles.
A method for single-pass image formation has been proposed for speed-up of printing in recent years. The method performs printing by a single pass using a plurality of heads having a plurality of nozzles arranged in the width direction of a sheet.
If the suction purge is used for the maintenance, a single-pass image forming device, which includes a plurality of nozzles corresponding to the size of a sheet in the width direction along its side and thus does not require a transfer in the width direction, requires close contact between recording heads having nozzles arranged in the width direction and a suction part and requires accuracy of alignment of the suction part with the nozzles. By contrast, the pressure purge enables an image forming device to perform maintenance more easily. Accordingly, single-pass image forming devices generally use the pressure purge as a maintenance method (e.g., Patent Literatures 1 and 2).
Instead of the maintenance by ink ejection, there is also a method for maintenance which removes air bubbles included in the ink in recording heads by returning the ink, which has been supplied to the recording heads, to an ink supplier reservoir part (i.e., return current maintenance).